1. Field of the Invention
The present invention is generally directed to read sensors for reading data from magnetic media. More specifically, the present invention is directed to a mechanism for stabilizing a giant magnetoresistive based read sensor in a read/write head of a magnetic media device.
2. Background of the Invention
The requirement of high density magnetic storage of data on magnetic tape and hard disk drives has been increasing steadily for the past several years. Magnetic tape and hard disk drives include magnetic heads for reading and writing data to the magnetic media. The magnetic heads include write coils and sensors for reading data from the magnetic media.
Development of magnetoresistive (MR) sensors (also referred to as heads) for magnetic media drives in the early 1990's allowed magnetic media drive products to maximize storage capacity with a minimum number of components (heads, disks, etc.). Fewer components result in lower storage costs, higher reliability, and lower power requirements for the magnetic media drives.
MR sensors are used for the read element of a read/write head on a high-density magnetic media drive. MR sensors read magnetically encoded information from the magnetic medium by detecting magnetic flux stored in the magnetic medium. As storage capacity of magnetic media drives has increased, the storage bit has become smaller and its magnetic field has correspondingly become weaker. MR heads are more sensitive to weaker magnetic fields than are the inductive read coils used in earlier magnetic media drives. Thus, there has been a move away from inductive read coils to MR sensors for use in magnetic media drives.
During operation of the magnetic media drive, sense current is passed through the MR element of the sensor causing a voltage drop. The magnitude of the voltage drop is a function of the resistance of the MR element. Resistance of the MR element varies in the presence of a magnetic field. Therefore, as the magnitude of the magnetic field flux passing through the MR element varies, the voltage across the MR element also varies. Differences in the magnitude of the magnetic flux entering the MR sensor can be detected by monitoring the voltage across the MR element.
As discussed above, MR sensors are known to be useful in reading data with a sensitivity exceeding that of inductive or other thin film sensors. However, sensor failures with respect to magnetic domain nucleation and bias-point variation are a leading cause of yield loss in the fabrication of MR sensors. Tape head applications, as opposed to disk, are especially demanding with respect to sensor yield. This is because a tape head integrates many MR sensors, all of which must yield for the head to yield.
With each new generation of product, track widths are narrowed and the number of sensors per head increase. Because of the magnetics in read head sensors, and the trend to increase the number of sensors per head, a change in MR technology from anisotropic magnetoresistive (AMR) read head sensors to giant magnetoresistive (GMR) read head sensors, also known as spin valves, is anticipated. In an MR sensor, such as an AMR sensor, a resistance change is caused by an intrinsic property of the sensing layer. In a GMR sensor, however, a resistance change is caused by the quantum nature of electrons. GMR sensors may have up to ten times the sensitivity of AMR sensors.
AMR and GMR sensors are composed of multiple thin films. Both sensors have a sensing layer that responds to external magnetic fields. In the absence of an external magnetic field, this sensing layer will spontaneously magnetize itself parallel with the long axis of this layer. A fixed magnetic field (“horizontal bias”) is also applied in this direction by hard bias films to establish a single magnetic domain in the sensing layer. This single magnetic domain minimizes domain noise and promotes consistent reading. This sensing layer's magnetic orientation, referenced to the magnetic media, rotates from parallel to perpendicular when an increasing perpendicular magnetic field (“transverse magnetic field”) is applied. This field is composed of a varying external magnetic field from the magnetic media and fixed internal magnetic fields (“transverse bias”) from other parts of the sensor.
The domain instabilities and bias-point variation of AMR read head sensors degrade with decreasing track width. Studies of AMR read head sensors indicate that the most likely cause in bias-point variation of these types of read heads is the type of permanent magnet technology that AMR sensors are constrained to use based on existing wafer film deposition systems. In addition to the intrinsic permanent magnet driven variations, extrinsic magnetic perturbations caused by scratches across the AMR sensor or electrostatic discharge (ESD) events are common causes of failures of these sensors.
Thus, it would be beneficial to have an apparatus and method for minimizing these instabilities and bias-point variations in read head sensors. More specifically, it would be beneficial to have an apparatus and method for minimizing these sources of failure in giant magnetoresistive (GMR) read head sensors.